TRUE. I found the problem in 3.3.2 and confirmed that the latest change for 3.4 doesn't address this problem. I suspect that the problem has potentially existed for a long time but was exacerbated by more recent code that sets the current user to 0.

I've added a new file which contains a test setting the user by name with ID=null.
and a test demonstrating that name is trumped by ID. e.g. wp_set_current_user( "admin", "bobbingwide" ); will return the "admin" user.

There seems little point in adding tests for setting it by a numeric ID, since this is already implicit in many other tests.

Previously, the name fallback was failing in the case where the current user
was 0, due to a loose comparison between 0 (the current user) and null (the
value that is used to trigger the name fallback).